When spending a day at the beach, a noticeable drop in temperature may
occur during the early afternoon as a cool
breeze begins to blow off of the water.
This wind is known as the "sea breeze", which occurs in response to
differences in temperature between a body of water and neighboring land.

Sea-breeze circulations most often occur on warm sunny days
during the spring
and summer when the temperature of the land is normally
higher than the temperature
of the water.
During the early morning hours, the land and
the water start out at roughly the same temperature.
On a calm morning, a given
pressure surface
will be at the same height
above both the land and water.

A few hours later, the
sun's energy begins to
warm the land more rapidly than the water.
By later in the day,
the temperature of the land increases while the temperature
of the water remains relatively constant.
This occurs because water,
especially large bodies of water like a lake or ocean,
are able to absorb
more energy than land without warming.

It is important to remember that the air is not heated
directly from
above by the sun. In fact, most of the incoming solar energy actually
passes right through the atmosphere.
However, as the land
absorbs this energy, heat is radiated back into
the atmosphere (from the earth), warming the overlying air.
Some of this heat is transported to
higher levels in the atmosphere through
convection.

On the other hand, since the temperature of the water remains
relatively constant throughout the day,
the air over the water is not heated from below (as over land), resulting
in lower air temperatures over the water.